Caption: Haemoglobin Rothschild molecule. Computer model of haemoglobin Rothschild (37 beta Trp----Arg), a mutant variant of normal haemoglobin. Haemoglobin is the principal protein component of red blood cells. Each molecule is made up of four subunits (coloured ribbon structures) called alpha and beta subunits. Within each subunit is an oxygen binding site, or haem group (turquoise). Each haem group contains one atom of iron (green). Haemoglobin transports oxygen around the body by binding one oxygen molecule to each haem group. In haemoglobin Rothschild, the mutation results in reduced oxygen affinity.